The invention relates to a positively operating radiation-sensitive mixture containing a photoactive component and a binder which is insoluble in water but soluble or at least swellable in aqueous-alkaline solution.
Radiation-sensitive mixtures which contain photoactive diazo derivatives and are suitable for irradiation with high-energy UV radiation have been described in the literature for some time.
Positively operating radiation-sensitive mixtures which contain a diazo derivative of Meldrum's acid as the photoactive compound are mentioned in U.S. Pat. No. 4,339,522. This compound is said to be suitable for exposure to high-energy UV radiation in the range from 200 to 300 nm. However, it has been found that when these mixtures are used, the photoactive compound is exuded under the relatively high processing temperatures frequently employed in practice; the radiation-sensitive mixture loses its original activity, so that reproducible structurings are not possible.
EP-A-0,198,674 and 0,262,864, U.S. Pat. No. 4,622,283 and SU-A-1,004,359 provide 2-diazo-cyclohexane-1,3-dione or -cyclopentane-1,3-dione derivatives as photoactive compounds for radiation-sensitive mixtures of the type described. These compounds have a lower volatility, but instead, depending on the substitution pattern present, exhibit a poor compatibility in the radiation-sensitive mixture. This manifests itself in particular by crystallization of the photoactive compound during drying of the layers, by insolubility thereof in solvents used in practice or by a layer inhomogeneity caused by phase separation.
Other positively operating photoactive compounds which are sensitive in the low UV range are known from EP-A-0,129,694 and U.S. Pat. No. 4,735,885. The compounds described in these documents have the disadvantage that the carbenes formed from them during exposure do not have a stability in the matrix which is adequate for the desired carboxylic acid formation. This leads to an inadequate solubility difference between the exposed and non-exposed areas in the developer and therefore to an undesirably high removal rate of the non-exposed areas. A possible explanation for this phenomenon is given by C. G. Willson et al. in SPIE Vol. 771, "Advances in Resist Technology and Processing IV", 2 (1987).
EP-A-0,195,986 therefore proposes .alpha.-phosphoryl-substituted diazocarbonyl compounds as photoactive compounds, since these have an increased carbene stability. In practice, however, such compounds probably find only minor use, since atoms which can potentially be used as doping agents, such as, for example, the phosphorus contained in these compounds, must be very meticulously excluded during the processing processes.
In their paper "Positive Excimer Laser Resist Prepared with Aliphatic Diazoketones" (SPIE Proc., 920, 51 (1988)), H. Sugiyama, E. Ebata, A. Mizushima and K. Nate introduce novel .alpha.-diazoacetoacetates which are employed as photoactive compounds in positively operating radiation-sensitive mixtures, in particular for use with radiation in the low UV range. Since these are derivatives of aceto-acetic acid, the keto group in the .beta.-position relative to the ester group is directly adjacent to a terminal methyl group. Radiation-sensitive mixtures which contain the compounds mentioned as photoactive components exhibit good bleaching properties, but their properties in respect of image differentiation are poor.